In a manufacturing process of semiconductor devices or a flat panel device (FDP), a plasma processing apparatus is widely used as an apparatus for performing etching, depositing, oxidizing, sputtering or the like. In the plasma processing apparatus, e.g., a plasma etching apparatus, an upper and a lower electrode are arranged in parallel in a processing chamber or an reactor; and a substrate to be processed (semiconductor wafer, glass substrate, or the like) is loaded on the lower electrode and a high frequency voltage for generating a plasma is applied to the upper or the lower electrode via a matching unit.
In general, a number of gas injection holes are provided on the upper electrode and an etching gas is injected from the injection holes over the entire upper surface of the substrate, thereby etching the surface of the substrate to be processed by a plasma of the etching gas.
Generally, an upper and a lower electrode of a parallel plate type plasma etching apparatus are disposed parallel to each other and a high frequency voltage for generating a plasma is applied to the upper or the lower electrode. Then, electrons accelerated by the high frequency electric field generated between the electrodes, and secondary electrons and thermal electrons emitted from the electrodes collide with and ionize molecules of processing gas, thereby generating a plasma of the processing gas. Thus, a required micromachining, e.g., an etching on a surface of the substrate, is executed by radicals and/or ions in the plasma.
Further, as semiconductor integrated circuits become finer and finer, the plasma processing is required to be conducted by using a high density plasma at a low voltage condition. For example, in a capacitively coupled plasma processing apparatus, high efficiency, high density, and low bias of the plasma processing are needed. Moreover, as the size of the semiconductor chip and the diameter of the substrate to be processed are getting larger, there are needed a plasma of a larger scale and thus a greater chamber (processing vessel).
However, in such a large-scaled plasma, an intensity of electric field at the center portion of an electrode (upper or lower electrode) tends to be greater than that at the peripheral portion thereof. As a result, there is a problem that a plasma density is higher at the center portion of the electrode than at the peripheral portion thereof, and thus resistivity of the plasma is low at the center portion of the electrode. As a consequence, a current concentrates at the center portion of the opposite electrode and the uniformity of the plasma density becomes worse.
Additionally, as the chamber gets larger, there is caused a problem that a plasma density becomes different at the center portion and at the peripheral portion of the substrate due to influence from a flow of the processing gas in an actual etching process.
The nonuniformity of the plasma density leads to discrepancies in an etching rate of the substrate, which may result in deteriorating a throughput of devices obtained from the peripheral portion of the substrate.
To address these problems, there have been various researches for a structure of the electrode. In order to cope with them, there is known a technology in which a central portion of a main surface of the high frequency electrode is made of a highly resistive material (see, e.g., Japanese Patent Application Publication No. 2000-323456). In this technology, the central portion of the main surface (a surface to which a plasma contacts) of the electrode to which a high frequency power supply is connected, is formed with the highly resistive material which dissipates larger high frequency power by joule heat. Therefore, an intensity of electric field on the main surface of the electrode is relatively lower at the center portion thereof than at the peripheral portion thereof, thereby correcting the nonuniformity in the plasma density.
Meanwhile, there is disclosed a plasma processing apparatus in which a dielectric is embedded in a main surface of an electrode facing a processing space (see, e.g., Japanese Patent Application Publication No. 2004-363552). In this technology, a uniformity of the plasma density is improved by making impedance of a high frequency power, which is radiated from the main surface of the electrode to the processing space, relatively large at the center portion of the electrode and relatively small at the peripheral portion thereof.
However, if the central portion of main surface of the high frequency electrode is formed by the highly resistive material in the above-mentioned high frequency discharging type plasma processing apparatus, there is a problem that dissipation of the high frequency power by joule heat (energy loss) is increased.
Further, since characteristics of the impedance distribution over the main surface of the electrode are fixed by a material and a shape profile of the dielectric in the above technology in which the dielectric is embedded in the main surface of the electrode, there is a drawback that it cannot adaptively deal with various processes or process conditions.